Crush resistance

[Thorfun]

hello boffins,

 

I'm hoping someone much cleverer than me can answer me what a value of 1000N/10 cm of crush resistance equates to? i.e. if a cable with that crush resistance was buried in the ground (clay) how far down would it need to be to not be subjected to that level of force?

[Radian]

18 minutes ago, Thorfun said:

hello boffins,

 

I'm hoping someone much cleverer than me can answer me what a value of 1000N/10 cm of crush resistance equates to? i.e. if a cable with that crush resistance was buried in the ground (clay) how far down would it need to be to not be subjected to that level of force?

1000N/10cm is 10N/1mm (sounds more butch over 10cm don't it). So you're looking at a point load of just over 1kg. Interesting but no answer to your question - which needs augmenting with the mass of the load, and the area it acts over. It could support any load you can dream of - if deep enough.

 

Or maybe you mean the load is just the weight of the clay above? I doubt that's what you mean.

(Oops, should have made that a 10kg point load)

Edited September 25, 2022 by Radian

[Thorfun]

5 minutes ago, Radian said:

1000N/10cm is 10N/1mm (sounds more butch over 10cm don't it). So you're looking at a point load of just over 1kg. Interesting but no answer to your question - which needs augmenting with the mass of the load, and the area it acts over. It could support any load you can dream of - if deep enough.

 

Or maybe you mean the load is just the weight of the clay above? I doubt that's what you mean.

so, I want to bury PE sheathed Cat6a cable (labelled as direct burial but can anyone blindly believe that). I am just wondering if it's worth spending £80 to 'protect' it in ducting from being crushed or if it will be ok direct buried? it will be about 500mm - 600mm below ground level and be buried under clay.

 

From the reading I've done PE sheathing is suitable for direct burial but I wondered if there was actual science and physics calculations to check at what point in depth the crush rating is exceeded!

[Radian]

Sorry if I alarmed you as I just spotted I should have made that a 10kg point load (now edited). Clay is liable to heave but it depends on what other structures may be present/crossing the cable. The crush rating could be exceeded at any depth by a suitably massive load above, so it's a bit of a 'how long is a piece of string' question - without saying something like 'to withstand vehicles parking on it', or 'foot traffic', or 'just to support the clay above'.

[ProDave]

If it says suitable for direct burying it will be.

 

What ducting will do for you, is enable you to replace it for a different type of cable when the "next thing" comes along.

[Onoff]

I used this solid DNO duct. The SWA runs in that. Then I've 20mm flex conduits within that with the Cat-5, screened flex etc in.

 

Think this was a tenner win on eBay. Add the petrol picking it up from Esher 😂

 

Edited September 26, 2022 by Onoff

[Thorfun]

50 minutes ago, Radian said:

Sorry if I alarmed you as I just spotted I should have made that a 10kg point load (now edited). Clay is liable to heave but it depends on what other structures may be present/crossing the cable. The crush rating could be exceeded at any depth by a suitably massive load above, so it's a bit of a 'how long is a piece of string' question - without saying something like 'to withstand vehicles parking on it', or 'foot traffic', or 'just to support the clay above'.

it will eventually be under a patio. so I guess there'll be hardcore compacted with a whacker plate at some point and after that it'll just be foot traffic. I wonder then if the question should what depth of clay is required to allow the crush rating to not be exceeding by a load of value x? I'm surprised there isn't some formula to calculate that sort of thing? isn't that what structural engineers do?

 

57 minutes ago, ProDave said:

If it says suitable for direct burying it will be.

and I want to believe the blurb! fyi this is the cable I've bought. I was just hoping that maths could give me more assurance than marketing material. 

 

50 minutes ago, ProDave said:

What ducting will do for you, is enable you to replace it for a different type of cable when the "next thing" comes along.

yeah, I get this, but the network cable is basically just going to end up at the chicken house for a PoE CCTV camera along with a 6mm SWA cable which I won't be running in ducting as our sparky says it's not worth it. which I agree with as SWA is fine buried! so I doubt I'll ever need to upgrade the network cable. I'm more concerned with potential damage as to dig it up to repair would be tricky. maybe I should've just forked out for the SWA Cat6 cable but it was double the price!

 

8 minutes ago, Onoff said:

I used this solid DNO duct. The SWA runs in that. Then I've 20mm flex conduits within that with the Cat-5, screened flex etc in.

 

I'm thinking of 40mm twin-wall ducting run alongside the SWA 6mm 3-core cable to run the Cat6a cable in. but, as @ProDave says, it says direct burial so maybe I should save myself the £80 and not be so paranoid and just bury the cable. 

[Onoff]

30 minutes ago, Thorfun said:

I'm thinking of 40mm twin-wall ducting run alongside the SWA 6mm 3-core cable to run the Cat6a cable in. but, as @ProDave says, it says direct burial so maybe I should save myself the £80 and not be so paranoid and just bury the cable. 

 

@ProDave went on to say that a duct will future proof the install. 

Edited September 25, 2022 by Onoff

[Thorfun]

41 minutes ago, Onoff said:

 

@ProDave went on to say that a duct will future proof the install. 

I know, but how much future proofing do chickens need? It’s not like they’ll need to start streaming 8k movies! 😂

[Thorfun]

ok, ok. you all win. I will disregard the crush resistance and run both the SWA 6mm 3-core and the PE sheathed Cat6a U/FTP cable in a 63mm duct and be dammed about the cost and the ramifications that might ensue!

 

(can you tell that my funds are running out?)

[TonyT]

Good shout 

[Onoff]

19 minutes ago, Thorfun said:

I know, but how much future proofing do chickens need? It’s not like they’ll need to start streaming 8k movies! 😂

 

Chicken Run?

[Thorfun]

12 minutes ago, TonyT said:

Good shout 

now I've just got to figure out how to get 2 x 63mm twinwall + 1 x 54mm  rigid  duct through a 150mm duct in to the basement! I'm thinking a nice 3D printed Y-branch should do the trick and I can put the 2 x 63mm twinwalls into the Y-branch and then I can fit them through the duct in to the basement.

 

nothing is easy is it?

[Thorfun]

maybe if I go down to 50mm twinwall (or maybe 40mm assuming the 32mm ID will accept the SWA and network cable) I could fit all three through the wall? will measure it tomorrow.

[Roundtuit]

Check ducting prices before you commit; last time I bought some from a merchant, bigger was cheaper due to the volumes they sold.

[Thorfun]

hope you're all happy now! 😂

 

 

it's like modern art.

 

currently 3D printing a bespoke reducing funnel to accept 5 ducts (these 4 x 63mm twinwalls plus another 54mm rigiduct) to allow the cables to feed through a 110mm twinwall duct going through to my basement. it's going to take a while to finish!

 

 

[Radian]

I bet you'll sleep better for having done it in conduit 😇

[Thorfun]

8 minutes ago, Radian said:

I bet you'll sleep better for having done it in conduit 😇

yeah. it was great advice and I'm much happier now. it was just the thought of having to dig up the SWA cable after partially filling it in and then digging a wider trench to accommodate the ducts that was putting me off. so much to do and so little time! but I now have the option of running more cable in the future if needed which is much better.

 

I also think I learnt something about crush resistance but I'm sure that'll be forgotten by tomorrow when I've moved on to the next problem that needs resolving!